Microfluidic device and a method of loading fluid therein

A microfluidic device, comprising:

• first and second substrates spaced from one another by a spacer and a fluid barrier, and side walls, the first substrate being an upper substrate and the second substrate being a lower substrate such that the first and second substrates and the side walls define a chamber therebetween;
• and
• a plurality of ports that permit introduction of fluid into the chamber and/or displacement of fluid from the chamber;
• the chamber including a vent area containing a venting fluid and an active area, and the plurality of ports includes at least one input port, a first vent port located in the vent area, and a second vent port located in the active area;
• wherein the active area of the chamber is configured to receive a filler fluid that is introduced into the active area of the chamber through one or more of the plurality of ports filling the active area of the chamber with the filler fluid, and the active area of the chamber is configured to receive a volume of an assay fluid introduced into the active area of the chamber through the at least one input port, and
• wherein the first vent port is positioned such that a portion of the venting fluid vents through the first vent port, and the second vent port is positioned such that a portion of the filler fluid is displaced into the second vent port, upon entry of the volume of the assay fluid into the chamber.